In the related art, in order to perform treatment such as hardening on a metal part that is a treatment object, a heat treatment device is used that includes a heating room and a cooling room. For example, Patent Document 1 discloses a heat treatment device in which heating rooms are provided above an intermediate transfer room and a cooling room is provided below the intermediate transfer room. In general, the cooling room of the heat treatment device or the like is provided with a coolant collection and supply device (a cooling medium circulator) that collects a coolant (a cooling medium) from the cooling room, cools the collected coolant and supplies the coolant to the cooling room. For example, the coolant collection and supply device includes a coolant tank that stores the coolant collected from the cooling room, a cooling pump that pumps the coolant stored in the coolant tank into header pipes (mist headers) of the cooling room, and a heat exchanger that cools the coolant pumped by the cooling pump. In addition, the cooling room is provided with, for example, mist nozzles (cooling nozzles) that spray, onto the treatment object, the coolant supplied from the coolant collection and supply device. The treatment object is deprived of heat through vaporization of the coolant sprayed from the mist nozzles and thus is cooled.